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Section 3. Epistemology. Descartes’ Doubt. If it is possible that I am dreaming now, then I have reasons to doubt whether my current perceptual beliefs are true. . Descartes’ Doubt.
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Section 3 Epistemology
Descartes’ Doubt • If it is possible that I am dreaming now, then I have reasons to doubt whether my current perceptual beliefs are true.
Descartes’ Doubt • If it is possible that I am dreaming now, then I have reasons to doubt whether my current perceptual beliefs are true. • It is possible that I am dreaming right now.
Descartes’ Doubt • If it is possible that I am dreaming now, then I have reasons to doubt whether my current perceptual beliefs are true. • It is possible that I am dreaming right now. • Therefore: I have reasons to doubt whether my current perceptual beliefs are true.
What is the form of this argument? • If it is possible that I am dreaming now, then I have reasons to doubt whether my current perceptual beliefs are true. • It is possible that I am dreaming right now. • Therefore: I have reasons to doubt whether my current perceptual beliefs are true.
What is the form of this argument? • If it is possible that I am dreaming now, then I have reasons to doubt whether my current perceptual beliefs are true. • It is possible that I am dreaming right now. • Therefore: I have reasons to doubt whether my current perceptual beliefs are true. • If p,
What is the form of this argument? • If it is possible that I am dreaming now, then I have reasons to doubt whether my current perceptual beliefs are true. • It is possible that I am dreaming right now. • Therefore: I have reasons to doubt whether my current perceptual beliefs are true. • If p, then q.
What is the form of this argument? • If it is possible that I am dreaming now, then I have reasons to doubt whether my current perceptual beliefs are true. • It is possible that I am dreaming right now. • Therefore: I have reasons to doubt whether my current perceptual beliefs are true. • If p, then q. • p.
What is the form of this argument? • If it is possible that I am dreaming now, then I have reasons to doubt whether my current perceptual beliefs are true. • It is possible that I am dreaming right now. • Therefore: I have reasons to doubt whether my current perceptual beliefs are true. • If p, then q. • p. • Therefore, q.
Modus Ponens • If it is possible that I am dreaming now, then I have reasons to doubt whether my current perceptual beliefs are true. • It is possible that I am dreaming right now. • Therefore: I have reasons to doubt whether my current perceptual beliefs are true. • If p, then q. • p. • Therefore, q.
Second Argument • It is impossible to distinguish with certainty between dream experiences and waking experiences.
Second Argument • It is impossible to distinguish with certainty between dream experiences and waking experiences. • If it is impossible to distinguish with certainty between dream experiences and waking experiences, then I cannot know whether I am awake right now.
Second Argument • It is impossible to distinguish with certainty between dream experiences and waking experiences. • If it is impossible to distinguish with certainty between dream experiences and waking experiences, then I cannot know whether I am awake right now. • If I cannot know that I am awake right now, then it is possible that I am dreaming right now.
Second Argument • It is impossible to distinguish with certainty between dream experiences and waking experiences. • If it is impossible to distinguish with certainty between dream experiences and waking experiences, then I cannot know whether I am awake right now. • If I cannot know that I am awake right now, then it is possible that I am dreaming right now. • Therefore it is possible that I am dreaming right now.
What is the form of this argument? • It is impossible to distinguish with certainty between dream experiences and waking experiences. • If it is impossible to distinguish with certainty between dream experiences and waking experiences, then I cannot know whether I am awake right now. • If I cannot know that I am awake right now, then it is possible that I am dreaming right now. • Therefore it is possible that I am dreaming right now.
What is the form of this argument? • It is impossible to distinguish with certainty between dream experiences and waking experiences. • If it is impossible to distinguish with certainty between dream experiences and waking experiences, then I cannot know whether I am awake right now. • If I cannot know that I am awake right now, then it is possible that I am dreaming right now. • Therefore it is possible that I am dreaming right now. • p.
What is the form of this argument? • It is impossible to distinguish with certainty between dream experiences and waking experiences. • If it is impossible to distinguish with certainty between dream experiences and waking experiences, then I cannot know whether I am awake right now. • If I cannot know that I am awake right now, then it is possible that I am dreaming right now. • Therefore it is possible that I am dreaming right now. • p. • If p, then q.
What is the form of this argument? • It is impossible to distinguish with certainty between dream experiences and waking experiences. • If it is impossible to distinguish with certainty between dream experiences and waking experiences, then I cannot know whether I am awake right now. • If I cannot know that I am awake right now, then it is possible that I am dreaming right now. • Therefore it is possible that I am dreaming right now. • p. • If p, then q. • If q, then r.
What is the form of this argument? • It is impossible to distinguish with certainty between dream experiences and waking experiences. • If it is impossible to distinguish with certainty between dream experiences and waking experiences, then I cannot know whether I am awake right now. • If I cannot know that I am awake right now, then it is possible that I am dreaming right now. • Therefore it is possible that I am dreaming right now. • p. • If p, then q. • If q, then r. • If p, then r (unstated)
What is the form of this argument? • It is impossible to distinguish with certainty between dream experiences and waking experiences. • If it is impossible to distinguish with certainty between dream experiences and waking experiences, then I cannot know whether I am awake right now. • If I cannot know that I am awake right now, then it is possible that I am dreaming right now. • Therefore it is possible that I am dreaming right now. • p. • If p, then q. • If q, then r. • If p, then r (unstated) • Therefore, r